Substrate Specificities of Octopine Dehydrogenases from Marine Invertebrates

-1. Amino acid, keto acid and imino acid substrate specificities of octopine dehydrogenase (ODH) from seven marine invertebrate sources were investigated. 2. Three groups of ODH enzymes were identified determined, largely, by their use of L-lysine as an alternative amino acid substrate, 3. The broadly specific ODH from the sea anemone, Calliactes parasitica, utilized L-arginine and L-lysine at equal rates showing a substrate site able to utilize both guanidino and non-guanidino amino acids. Keto acid specificity was also broad; apparent K,.'s for pyruvate, oxaloacetate and ct-ketobutyrate were similar. Both D-octopine and D-lysopine were oxidized by the enzyme. 4. ODH from 3 bivalves, Mytilus edulis, Cerastoderma edule and Glycymeris glycymeris and from the cephalopod, Sepia officinalis showed lower rates of enzyme activity with L-lysine or L-ornithine (3-79~o of L-arginine activity), lower rates with alternative guanidino amino acids, L-homoarginine and L-canavanine, and higher apparent K,,'s for alternative keto acids compared to the sea anemone enzyme. Mantle muscle ODH from S. officinalis, with its major physiological role in glycolytic energy production during burst swimming, showed the highest specificity for L-arginine of all enzymes examined. 5. ODH from the bivalve, Arctica islandica, showed no activity in the presence of non-guanidino amino acids. 6. The evolutionary development of the ODH enzyme appears to have led from a broadly specific imino acid dehydrogenase in sea anemones to enzymes increasingly specific for the substrates L-arginine and pyruvate only. This trend is correlated with an increasing importance of ODH in glycolytic redox balance in working muscle and an increased dependence on muscle arginine phosphate reserves for rapid energy generation in higher invertebrate groups.